1. Field of the Invention
The present disclosure relates to improved methods for sealing plastic bags, and in particular plastic bags with pinch ends.
2. Background of the Invention
Conventional plastic bags of a wide variety of size and shape are used in various situations. Bulk materials, such as flour, sugar, rice, seed, animal feed, chemicals, powdered materials or the like, for example, typically have been packaged in woven plastic bags in the past. Pet food, bird seed and other products sold in retail stores typically have not been packaged in conventional woven plastic bags. Among other reasons for this, woven plastic bags were considered too rudimentary to be printed with high end graphics suitable for consumer type of packaging. In addition, the high speed requirements in the filling and packaging operations limited the use of the woven bags in these applications.
Laminated woven sacks (LWS) were developed using a woven polypropylene structure laminated to a bi-oriented polypropylene film (BOPP) that can be reverse printed with high end graphics suitable for consumer type of packaging. The LWS provides a stronger, more attractive bag than the more conventional multiwall bags used for that purpose over the last 20 years. Due to their tough strong structure, conventional LWS bags are typically sewn shut on both ends. These LWS recently met with success and have been successfully substituted for the conventional multiwall paper bags used in the pet food industry for many years.
One major drawback of the sewn LWS has been the closing of the bags at high speed filling lines, such as those for filling such bags with pet food. Experience has shown that sewing production lines are typically slower than the filling of the multiwall pinch bottom bags. Additionally, the sewn bags do not provide an aesthetically pleasing and useful clean display on the ends of the bags, thus making it difficult for consumers to identify or find a desired brand quickly when the bags are displayed on the shelves at the point of sale, such as when they are stacked on top of one another. In addition, the sewn ends required puncturing the plastic bags and thus result in a bag that is not sealed, leading to somewhat reduced shelf-life and possible infestation of the contents of the bag. Other methods for sealing woven and non-woven plastic bags include sealing with a single or double fold at each end with tape over the single or double fold, or a zipper at one end and a single or double fold at the other end. However, these methods also slow down production and/or add cost to the manufacture of the plastic bag. Thus, there is a need for pinch laminated woven sacks that overcome these drawbacks in the filling and closing operations while allowing an attractive graphic display of the end of the bag at the retail outlet and also providing a strong, durable bag that remains sealed.
Woven plastic bags have been used and are conventional for certain applications. An example of a conventional woven plastic bag is provided in U.S. Pat. No. 4,373,979 (“the '979 patent”), issued on Feb. 15, 1983. The '979 patent describes the use of woven strips of highly longitudinally-oriented, high-density polyethylene or polypropylene in a bag construction in which the bag is formed from a seamed tube made of the woven plastic material. The seamed tube has gussets on either side and, when a portion is cut from the rest of the tube, a bag having two open, unsealed ends is provided. The '979 patent describes the use of ultrasonic spot welds to seal portions of a bag made of such woven plastic strips, as opposed to sewing the seams of a bag or using a hot melt adhesive to seal the gusset forming pleat. The '979 patent is hereby incorporated by reference herein. The '979 patent purports to be an improvement for sealing a plastic bag. As noted in the '979 patent, sewing one end tends to take longer, thus adding time to the manufacturing process. In addition, the sewn ends in a conventional bag tend to be a weak portion of the bag, and a likely location for rips, tearing, and subsequent loss of contents during storing, shipping and handling. In addition, such bags may not provide sufficient protection from infestation from vermin and/or insects.
Another example of plastic bags is disclosed in U.S. Patent Application Publication Number U.S. 2010/0029455 A1 (“the '455 publication”), published on Feb. 4, 2010, which describes production of web sections from a flexible web material that is provided with tear-off lines produced by laser beam processing at the distance of the length of the web sections to be formed. The tear-off lines weaken the flexible web material, but do not result in complete separation of the web sections from the web material, which occurs upon tearing the flexible web material. The '455 publication is incorporated by reference herein.
More recently, some types of plastic bags have provided improvements in sealing the ends of the bags. For example, in U.S. Pat. No. 6,800,051 B2 (“the '051 patent”), issued on Oct. 5, 2004, a process for sealing side fold sacks made of plastic film is described. According to the '051 patent, a web of plastic tubular film is cut to provide a staggered detachment along a perforation so that one wall (e.g., the front wall) projects beyond the opposing wall (e.g., the back wall). The projecting portion of the first wall is then folded over and sealed to the opposing wall by means of a plastic adhesive such as a polyurethane adhesive or hot melt. The '051 patent is hereby incorporated by reference herein. However, such bags involve plastic films, not woven plastic materials, and therefore are unable to handle the weight loads of conventional bulk bags made of paper and other materials. Such bags are useful for only certain lightweight contents, such as bread.
There are a variety of conventional ways of providing for reusable openings in bags. For example, U.S. Pat. No. 6,478,465 B1 (“the '465 patent”), issued Nov. 12, 2002, describes a peelable opening in a multiwall, pinched bottom open mouth bag construction. The '465 patent also describes the use of an adhesive layer that can be used so that the bag opening is reclosable. The '465 patent is hereby incorporated by reference herein.
Therefore, what is needed are improved methods for sealing woven and non-woven plastic bags that do not add much to the cost or time to manufacture, and are not susceptible to inadvertent tearing, punctures, breaking, or the like.